Too Much of a Good Thing

Even with compost you can overdo it

By Dr. Francis Gouin

Recently a Bay Weekly reader complained she could not grow cauliflower or broccoli. The plants grew big and lush but never produced edible heads — all this despite the large amount of compost she added to her garden soil each year.
My response was too much of a good thing. Compost is a good source of not only long-lasting fiber but also slow-release nutrients. For every percent of organic matter in soil, an acre of soil generates 10 pounds of nitrogen each year. If your soil contains five percent organic matter, that translates to 50 pounds of nitrogen per acre per year.
Growing a good crop generally requires between 100 to 120 pounds of nitrogen per acre per year. If your soil contains 12 percent organic matter, you should not have to apply any nitrogen fertilizer to achieve optimum plant growth — providing all other nutrients are present at optimum levels. If your garden soil contains 15 percent organic matter or more, plants are likely to produce super-lush growth. Leafy plants such as lettuce, cabbage, spinach, Swiss chard, celery and fennel should produce bumper crops. Cauliflower, broccoli, tomatoes, peppers and okra will likely produce large vigorous plants but limited fruit.
This same problem occurs when you apply too much nitrogen fertilizer. Several years ago a Bay Weekly reader complained that his tomato plants grew like trees but hardly produced any tomatoes. As I was not able to diagnose the problem, based on our discussion over the telephone, I invited him to Upakrik Farm and requested he bring the bags of fertilizer he used. He brought a bag of 10-10-10 and a bag of urea. He said he used urea and not calcium nitrate as I had recommended in one of my Bay Gardener articles because the store manager said calcium nitrate was not available but urea would substitute. Urea contains 45.5 percent nitrogen while calcium nitrate only contains 15.5 percent nitrogen. In other words, the excessive amount of nitrogen from the urea caused the tomato plants to remain vegetative rather than producing fruit. Monitoring organic matter content in your soil is another good reason for having periodic soil tests, which also measure pH and nutrient levels.

Are Strawberries Perennial?

Q If you want to get several years of picking strawberries from the same plants, would you leave them alone after picking or would you mow the top leaves off? I know that the commercial guys plow them under each year and replant for the next year, but I had a decent crop this year and hate to till them in.

–Frederic Ames, Shady Side

A The traditional method of growing strawberries is to rototill under the mother plants, leaving the daughter plants to produce next year’s crop. By doing so, the same bed can produce berries for three to four consecutive years. However, crown mites, often called cyclamin mites, cause crop failure on the fourth year.

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